A casting method for ultra-thick high-strength rack steel

Abstract

This invention discloses a casting method for ultra-thick high-strength rack steel, comprising: (1) a completely oxidation-free casting process, in which molten steel enters the bottom pouring tank from the ladle through the protective sleeve of the ladle, and then enters the mold cavity through the slurry channel; the side is a special series of refractory materials and steel structure mold, and the bottom is a cooling base plate; (2) the side of the mold is made of special refractory material, and the surface of the molten steel is made of low thermal conductivity carbonized rice husk; (3) the hot surface working layer material is used for ≥8h under working conditions of 1550℃, and the cold end temperature of the nano-insulation layer is ≤200℃ under equilibrium conditions; (4) the cooling base plate is a large-size water-cooled copper plate, the water velocity is ≥7m / s, and the surface temperature of the copper plate during the casting process is ≤300℃; (5) the cast ingot is demolded after cooling for ≥8h; (6) the ultra-thick billet with a diameter of ≥600mm is tested to have no shrinkage cavities, the central porosity is ≤0.5 grade, and the central segregation is ≤C0.5 grade. The advantages of this invention are that it improves the core mechanical properties of ultra-thick steel plates and reduces production costs.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a casting method for ultra-thick high-strength rack steel. Background Technology

[0002] The steel used in offshore platforms generally suffers from low strength, incomplete specifications, and poor corrosion resistance, making it difficult to achieve a stable product supply. This is especially true for ultra-high-strength marine engineering steel (≥150mm), which lacks core toughness and exhibits unstable Z-axis properties. Furthermore, the long procurement cycle and high cost of imported rack steel significantly hinder the development of marine engineering.

[0003] Since the thickness of plates produced by continuous casting equipment currently does not exceed 470mm, it is difficult to guarantee the quality of continuously cast thick plates. For thicker billets, three production methods are generally used: ingot casting slabs, ingot casting round ingots, and electroslag remelting billets.

[0004] Severe segregation in ingot-cast slabs easily leads to porosity and shrinkage cavities, which cannot be healed during rolling, affecting steel plate quality. Forging round ingots using a hydraulic press incurs costs over 2000 yuan / ton, with a 30% removal rate and low yield. Electroslag remelting billets can produce high-quality wide and thick slabs, but it is inefficient, requiring over 20 hours and incurring high manufacturing costs. In recent years, some steel mills have adopted vacuum welding of multiple slabs followed by rolling to produce extra-thick plates, but this method involves numerous processing steps, difficult flaw detection, and can only produce ordinary carbon steel, limiting its widespread application.

[0005] Typically, ultra-thick steel plates are produced using traditional methods of smelting, billet casting, and rolling. Due to the solidification characteristics of ingot casting and continuous casting processes, macroscopic segregation and inclusions are easily generated in the center of the billet, causing differences in properties across different parts of the billet. This leads to uneven stress during rolling and even billet cracking, which is inherited by the final ultra-thick steel plate product, reducing impact and tensile properties and posing potential risks to the service life of ultra-thick steel plates. Furthermore, the cost of electroslag ingot technology is more than 3000 yuan / ton higher than other processes. Existing ingot casting and continuous casting technologies struggle to meet the defect control requirements at the center of the billet, and the cost of electroslag ingots is too high. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of high defects, poor uniformity, and high cost of existing ultra-thick steel plates. It provides a casting method for ultra-thick high-strength rack steel, which significantly improves the core mechanical properties of ultra-thick steel plates, significantly improves the Z-axis properties of steel plates and the uniformity of properties of different thicknesses, reduces the cost of alloy design and heat treatment processes, ensures the stable preparation of high-quality billets with low defects, high uniformity, and low cost, and realizes the highly homogeneous production of steel ingots ≥600mm.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A casting method for ultra-thick high-strength rack steel, specifically comprising: (1) The whole process is oxidation-free casting. The molten steel enters the bottom pouring tank from the ladle through the protective sleeve of the ladle. The surface of the molten steel in the bottom pouring tank is isolated from the air by a special covering agent. Then it enters the inner cavity of the mold through the slurry channel. The side is a special series of refractory and steel structure mold, and the bottom is a cooling base plate used to cool the molten steel in the inner cavity of the mold. (2) The sides of the mold are made of special refractory material to provide heat insulation. This material includes a nano-insulation layer, a silicon-aluminum insulation layer, a polycrystalline insulation layer, and a hot working layer. The molten steel surface is made of carbonized rice husk with a low thermal conductivity, with a thickness of 10~30mm and a thermal conductivity ≤0.1W·m. -1 ·K -1 The lower the thermal insulation coefficient of the sidewall refractory material, the less segregation of the cast billet, and the better the internal quality. (3) By optimizing the design of the refractory material on the side of the mold, the hot surface working layer material can be used for ≥8h under working conditions of 1550℃, and the cold end temperature of the nano insulation layer is ≤200℃ under equilibrium conditions. (4) The cooling base plate is a large-size water-cooled copper plate with a water velocity of ≥7m / s and a copper plate surface temperature of ≤300℃ during the casting process; (5) By reasonably controlling the casting process, the cast ingot is demolded after cooling time ≥ 8 hours; (6) The extra-thick billet with a diameter of ≥600mm is tested to be free of shrinkage cavities, with central porosity ≤ 0.5 grade and central segregation ≤ C 0.5 grade.

[0008] Furthermore, the thickness of the nano-insulation layer is 10~20mm, the fire resistance is ≥1000℃, and the thermal conductivity is ≤0.1W·m. -1 ·K -1 .

[0009] Furthermore, the silicon-aluminum insulation layer has a thickness of 60-80 mm, a fire resistance of ≥1400℃, and a thermal conductivity of ≤0.2 W·m. -1 ·K -1 .

[0010] Furthermore, the polycrystalline insulation layer has a thickness of 30-50 mm, a fire resistance of ≥1500℃, and a thermal conductivity of ≤0.2 W·m. -1 ·K -1 .

[0011] Furthermore, the thickness of the hot-face working layer material is 20~40mm, the refractoriness is ≥1550℃, and the thermal conductivity is ≤1.0W·m. -1 ·K -1 .

[0012] Furthermore, the nano-insulation layer has a fire resistance of 1000℃ and a thermal conductivity of 0.02 W·m. -1 ·K-1 The silicon-aluminum insulation layer has a fire resistance of 1400℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The polycrystalline insulation layer has a fire resistance of 1530℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The refractoriness of the hot-face working layer material is 1570℃, and its thermal conductivity is 0.95 W·m. -1 ·K -1 .

[0013] Furthermore, the cooling base plate has a thickness of 35-50mm, a width of 2000-2700mm, a length of 3000-3800mm, and a back plate of 100-120mm.

[0014] Furthermore, the water velocity of the cooling base plate is guaranteed to be 9 m / s, and the copper plate temperature is 180°C during the casting process.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: (1) The method of the present invention can produce slabs with a thickness of 500~700mm and a single weight of 30~50t, realize the high homogeneity production of steel ingots with a thickness of ≥600mm, and can also cast small batches of high-value-added steel grades that cannot be produced by continuous casting processes, such as high manganese, high aluminum, and high titanium. (2) This invention changes the traditional casting cooling mode of billet. By controlling the heat transfer during the solidification process of molten steel, the position of the solidification end is adjusted to move to the top of the ingot. During the directional solidification process, the melt solidifies in the opposite direction to the heat flow. The center of the billet solidifies before the surface, which solves the problem of difficult feeding at the center of the ingot. This effectively controls the V-shaped and inverted V-shaped segregation in the ingot. (3) The extra-thick directional solidified billet produced by the present invention has no central segregation, good core quality, and dense and uniform structure, which is significantly better than continuous casting billets and traditional ingot casting. (4) The extra-thick billets produced by the directional solidification technology of the present invention do not require forging or billet preparation, and especially compared with electroslag remelting, the cost of alloy design and heat treatment processes is greatly reduced. (5) This invention achieves argon protection during the entire casting process, avoiding secondary oxidation of molten steel and resulting in high product purity; (6) This invention controls the unidirectional heat transfer during the solidification process of molten steel, with the solidification front advancing unidirectionally from bottom to top and the solidification end located at the top of the ingot. The core quality of the cast billet is significantly better than that of other processes, greatly improving the core mechanical properties of extra-thick steel plates and significantly improving the Z-axis properties and the uniformity of properties at different thicknesses. The extra-thick steel plates produced by this invention using directional solidification technology have high strength, high homogeneity, and high Z-axis properties, which is advantageous for the production of extra-thick steel plates such as rack steel. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the directional solidification casting structure of the present invention; Figure 2 This is a schematic diagram showing the distribution of the special refractory material of the present invention; Figure 3 This is a low-magnification mass image of the extra-thick billet produced in Embodiment 1 of the present invention. Detailed Implementation Example

[0017] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a casting method for ultra-thick high-strength rack steel according to the present invention. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0018] A casting method for ultra-thick high-strength gear steel, characterized in that: (1) Directional solidification casting system, such as Figure 1 As shown, the entire process is oxidation-free casting. Molten steel enters the bottom pouring tank 4 from the ladle through the ladle protective sleeve 5. The surface of the molten steel in the bottom pouring tank is isolated from the air by a special covering agent. Then, it enters the inner cavity 2 of the mold through the slurry channel 6. The sides are made of special series refractory material 3 and steel structure mold 1, and the bottom is a cooling base plate 7, which is used to cool the molten steel in the inner cavity 2 of the mold. (2) The sides of the mold are made of special refractory material 3, which serves as heat insulation. Its specific structure is as follows: Figure 2 As shown: The nano-insulation layer 31 has a fire resistance of 1000℃ and a thermal conductivity of 0.02 W·m. -1 ·K -1 The silicon-aluminum insulation layer 32 has a fire resistance of 1400℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The polycrystalline insulation layer 33 has a fire resistance of 1530℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The hot working layer material 34 has a refractoriness of 1570℃ and a thermal conductivity of 0.95 W·m. -1 ·K -1 The molten steel surface is coated with low thermal conductivity carbonized rice husk 8, with a thickness of 20 mm and a thermal conductivity of 0.08 W·m. -1 ·K -1 The lower the thermal insulation coefficient of the sidewall refractory material, the less segregation occurs in the cast billet, and the better the internal quality. (3) The cooling base plate 7 is a large-size water-cooled copper plate with a thickness of 45mm, a width of 2700mm, a length of 3800mm, a back plate of 120mm, a water velocity of 9m / s, and a copper plate temperature of 180℃ during the casting process. (4) Mold steel structure design, optimized comprehensive configuration of furnace lining materials, hot surface working layer material 34 used for 9 hours under working conditions of 1550℃, and cold end temperature of nano insulation layer material 31 150℃; (5) By reasonably controlling the casting process, the cast ingot is demolded after cooling time ≥ 8 hours; (6) For example Figure 3 As shown, the 630mm thick billet has no shrinkage cavities, a central porosity of grade 0.5, and a central segregation of grade C of grade 0.5.

[0019] The steel grade F690 is cast on-site, and the final steel plate has a yield strength ≥710MPa, tensile strength ≥800MPa, elongation ≥18%, reduction of area 60~75%, core impact energy ≥100J at -60℃, and CTOD characteristic value of 0.15~0.5mm when the heat input is 30KJ / cm.

[0020] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A casting method for ultra-thick high-strength gear steel, characterized in that, include: (1) The entire process is oxidation-free casting. Molten steel enters the bottom pouring tank from the ladle through the protective sleeve of the ladle. The surface of the molten steel in the bottom pouring tank is isolated from the air by a special covering agent. Then it enters the inner cavity of the mold through the slurry channel. The sides are made of special series of refractory and steel structure molds, and the bottom is a cooling base plate to cool the molten steel in the inner cavity of the mold. (2) The sides of the mold are made of special refractory material, which includes a nano-insulation layer, a silicon-aluminum insulation layer, a polycrystalline insulation layer and a hot working layer. The surface of the molten steel is made of carbonized rice husk with low thermal conductivity, with a thickness of 10~30mm and a thermal conductivity ≤0.1W·m. -1 ·K -1 ; (3) By optimizing the design of the refractory material on the side of the mold, the hot surface working layer material can be used for ≥8h under working conditions of 1550℃, and the cold end temperature of the nano insulation layer is ≤200℃ under equilibrium conditions. (4) The cooling base plate is a large-size water-cooled copper plate with a water velocity of ≥7m / s and a copper plate surface temperature of ≤300℃ during the casting process; (5) By reasonably controlling the casting process, the cast ingot is demolded after cooling time ≥ 8 hours; (6) The extra-thick billet with a diameter of ≥600mm is tested to be free of shrinkage cavities, with central porosity ≤ 0.5 grade and central segregation ≤ C 0.5 grade.

2. The casting method for ultra-thick high-strength gear steel according to claim 1, characterized in that: The thickness of the nano-insulation layer is 10~20mm, the fire resistance is ≥1000℃, and the thermal conductivity is ≤0.1W·m. -1 ·K -1 .

3. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The silicon-aluminum insulation layer has a thickness of 60-80mm, a fire resistance of ≥1400℃, and a thermal conductivity of ≤0.2W·m. -1 ·K -1 .

4. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The polycrystalline insulation layer has a thickness of 30-50 mm, a fire resistance of ≥1500℃, and a thermal conductivity of ≤0.2 W·m. -1 ·K -1 .

5. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The thickness of the hot-face working layer material is 20~40mm, the refractoriness is ≥1550℃, and the thermal conductivity is ≤1.0W·m. -1 ·K -1 .

6. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The nano-insulation layer has a fire resistance of 1000℃ and a thermal conductivity of 0.02 W·m. -1 ·K -1 The silicon-aluminum insulation layer has a fire resistance of 1400℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The polycrystalline insulation layer has a fire resistance of 1530℃ and a thermal conductivity of 0.12 W·m. -1 ·K -1 The refractoriness of the hot-face working layer material is 1570℃, and its thermal conductivity is 0.95 W·m. -1 ·K -1 .

7. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The cooling base plate has a thickness of 35-50mm, a width of 2000-2700mm, a length of 3000-3800mm, and a back plate of 100-120mm.

8. The casting method for ultra-thick high-strength rack steel according to claim 1, characterized in that: The water velocity of the cooling base plate is guaranteed to be 9 m / s, and the copper plate temperature is 180℃ during the casting process.

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